The binding specificity of rhesus antibodies elicited by various conjugate vaccines of group B Neisseria meningitidis (GBNM) was studied using a variety of group B meningococcal polysaccharide (GBPS) antigen systems. The antibody response, as measured by ELISA, was significantly higher to the spacer-containing GBPS or N-propionylated version of GBPS than to the native GBPS complexed with methylated human serum albumin (HSA). The specificity of a population of antibodies directed to the spacer, ADH, was confirmed by their binding to an unrelated pneumococcal 9V polysaccharide conjugated to HSA through ADH. Antibodies elicited by GBPS-OMV conjugate vaccine also showed binding to N-propionylated GBPS conjugated to HSA. Pooled sera of high responders from various vaccine groups showed varied degree of opsonophagocytic activity in presence of monkey complement. As an extension of the previous immunization schedule, four groups of monkeys were further immunized first with the purified GBPS alone at week 50 and then with killed whole cell vaccine of GBNM at week 72. While the booster immunization with pure GBPS did not increase the capsular antibody levels significantly, immunization with killed cells produced antibodies to the whole cell antigen. Neither multiple immunizations with the conjugates nor reimmunization with GBPS or killed whole cell vaccine resulted in any discernible safety-related symptoms in the monkeys.